Isotopendilution

Isotopendilution, commonly referred to as isotope dilution analysis (IDA) or isotope dilution mass spectrometry (IDMS), is a quantitative analytical technique that uses an isotopically enriched standard added to a sample to enable accurate measurement of an element or compound. The method is valued for its ability to correct for matrix effects and recovery losses during sample processing.

Principle: A spike containing the element of interest in a known, enriched isotopic form is added to the sample. The spike mixes with the native analyte, and the combined mixture is analyzed with an isotope-sensitive detector such as a mass spectrometer. Because the spike and the native analyte behave identically during chemical processing, the ratio of the isotopes (and/or the ratio of the overall signal to the spike signal) reflects the original amount of analyte in the sample. Using the known spike concentration and the measured isotope ratios, the initial analyte concentration is calculated with mass-balance equations.

Procedure: Identify the target element, prepare a precisely known isotopic spike, and add it to the sample. After thorough mixing, the sample is prepared for analysis (digestion or dissolution if needed). The isotopic composition is measured by mass spectrometry (e.g., ICP-MS, GC-MS, or LC-MS). The data are then processed to compute the analyte concentration based on the measured isotope ratios and the spike quantity.

Applications, advantages, and limitations: Isotopendilution offers high accuracy and robustness against matrix effects, making it suitable for trace analysis in environmental, clinical, geological, and materials contexts. It requires access to suitable isotopically enriched spikes and precise mass spectrometric measurement, and can be costly. Potential limitations include isotope interferences, instrumental bias, and the need for careful calibration and data analysis.

Related terms include isotope dilution mass spectrometry and IDMS, which emphasize the instrumental approach to the same fundamental principle.